Bumblebee response to glyphosate application within managed forests of New Brunswick, Canada

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University of New Brunswick
Pesticides are used to target undesired pests, but their use can also affect non-target organisms. Non-target effects can be both direct (such as a toxic response) or mediated effects, where the response from the focal community is observed because of changes within another community. Herbicide use in managed forests occur in late summer/ early fall when some pollinators are still flying and foraging. This puts them at risk of direct exposure to spray either during the application or after through contact with residues in pollen and nectar resources. Pollinators also rely on the plant community and alterations to the plant community structure from herbicide applications could influence pollinator responses. To test for this, I assessed bumblebee community patterns in forest blocks sprayed with a glyphosate-based herbicide and unsprayed (control) blocks. Overall, there were more individual bumblebees caught in sprayed blocks, but higher richness in unsprayed blocks. Bumblebee response to herbicide use was not significant between application and the bumblebee community (direct) but was observed when mediated through changes within the floral community. Herbicide application significantly increased cover of flowering plants and this resulted in higher abundance and diversity of bumblebees. Overall, the use of minor canopy disturbances (such as herbicide application) following the creation of early successional stands (from clearcutting) benefit plant species that bumblebees use, and this can result in increases in abundance and diversity.